(a) Technical Field
The present invention relates to a method for preparing a styrene-butadiene copolymer that can be used as an industrial material for tires, belts, hoses, etc., and a styrene-butadiene copolymer prepared by the same.
(b) Background Art
Styrene-butadiene copolymers or styrene-butadiene-polar monomer copolymers are mainly prepared by emulsion polymerization. These copolymers are used for tires, coating materials, toners, or the like. Several patents are disclosed about the techniques of preparing the styrene-butadiene copolymer or the styrene-butadiene-polar monomer copolymer by emulsion polymerization.
For example, U.S. Pat. Nos. 3,575,913 and 3,563,946 disclose preparation of a styrene-butadiene or styrene-butadiene-acrylate copolymer in emulsion state using potassium persulfate or azobisisobutyronitrile. U.S. Pat. No. 4,064,081 discloses emulsion polymerization of a butadiene-styrene copolymer using potassium persulfate as a polymerization initiator. U.S. Pat. Nos. 5,274,027 and 5,302,655 describe preparation of a styrene-butadiene-acrylate copolymer by emulsion polymerization from acrylate monomers such as itaconic acid, methyl methacrylate, etc., by using, for example, an ammonium persulfate initiator.
U.S. Pat. Nos. 6,512,053 and 6,716,925 describe preparation of a styrene-butadiene-acrylate copolymer by emulsion polymerization from hydroxyalkyl acrylate monomers such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and hydroxymethylmethacrylamide, by using, for example, an ammonium persulfate initiator.
Those styrene-butadiene copolymers prepared by emulsion polymerization have poor affinity for silica and improvement of polarity is required to improve the affinity. However, since the vinyl carboxylic acid monomer is poorly reactive and interferes with micelle formation by changing acidity, there is a limitation in removing the residual monomers. In order to improve the silica affinity, it is required to increase the content of the polar monomer, which makes processing of the melt blend difficult. As a result, compound viscosity and hardness become very high.
Further, the functional monomers of the above-mentioned patents do not have emulsifying capability, and thus there is emulsion stability problem when the amount of the emulsifier is reduced.
In the tire industry, there is a growing need for the development of styrene-butadiene rubbers having polar groups and silica composites with a structure suitable for the manufacture of silica tires.